Dear Ulrich, You are quite correct, I must be getting old and senile!
Best wishes, George Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-3021 or -3068 Fax. +49-551-39-22582 <CCP4BB@JISCMAIL.AC.UK> On Thu, 23 Jul 2009, Baumann Ulrich wrote: > > Dear George, > > did you mean 4n+2 accidentally missing -- 00l reflections 4n+1 or 4n+3 should > be systematically absent in P212121 anyway. > > Probably I misunderstood something. > > Thank a lot, > Ulrich > > > > > Quoting "George M. Sheldrick" <gshe...@shelx.uni-ac.gwdg.de>: > > >It appears that P212121 twinned so that the apparent space > >group is P43212 or P41212 is more common than I had realized. > >This requires that two axes are approximately equal in length > >and that the reflections 00l with l=4n+1 and l=4n+3 are > >'accidentally' missing. It is possible that in such cases > >translational NCS causes both the twinning and the apparent > >absences, and in addition it can disturb the statistical > >tests for twinning. These problems are likely to be more > >acute when the resolution of the data is relatively low. > > > >George > > > >Prof. George M. Sheldrick FRS > >Dept. Structural Chemistry, > >University of Goettingen, > >Tammannstr. 4, > >D37077 Goettingen, Germany > >Tel. +49-551-39-3021 or -3068 > >Fax. +49-551-39-22582 > > > > > > -- > ======================================== > Ulrich Baumann > University of Berne > ulrich.baum...@ibc.unibe.ch > phone + 41 31 631 4320/4343 > fax + 41 31 631 4887 >
